Research on aging in people suggests a number of characteristic changes in social and affective behaviors, including aggressiveness, fearfulness, and irritability. A comprehensive and richly-detailed analysis of the structure and functions of aggression and defense in rats has been developed with N.I.M.H. support. This analysis, which includes consideration of both the situational and experiential factors in these behavior patterns, and which has also been successfully applied to literature on the physiological correlates of aggression and defense, promises to provide meaningful parallels to human behavior patterns. This analysis serves as the core of the present proposal. In order to describe systematic changes in affective and social behaviors as a function of aging and senesence, adult life span behaviors of laboratory and wild rats will be examined in settings designed to adequately represent important features of the natural environment. Multiple measures will be taken of a variety of social and agonistic behaviors previously validated in both laboratory and wild rats. These measures may be analyzed so as to permit isolation of changes in aggressiveness, fearfulness or irritability as opposed to changes which may result from alteration of general activity levels or sensory abilities in aging rats.